1. Field of the Invention
This invention relates to high definition colour correction, for example used in conjunction with telecine scanning equipment.
2. Description of Related Art
There are known machines specifically designed to transfer images on film to electrical signals which can be used either for broadcasting or for capturing onto video tape. These machines are known as telecine machines. Examples of such machines are the Rank Cintel URSA machine, or the FDL90 machine as manufactured by Broadcast Television Systems (known as BTS) in Germany.
These machines quite often have associated systems known as colour correctors. These correctors take the resultant electrical systems from the telecine machine and process or alter some or all of the colours in the pictures. For example, such a system would be able to manipulate the red coloured areas in a scene, but leave the rest of the colours in the picture unaltered. A number of such machines exits, including the DCP manufactured by Pandora International of Kent, England or the Da Vinci Renaissance System, manufactured by Colorgraphics of Fort Lauderdale, Fla., USA.
It is normal to use a telecine machine and colour corrector in a `rehearse and playback` mode, under the control of a `programmer`. In this mode of operation there is first `reharsed` the grading of the film. This is typically done by running the film through the telecine, and identifying scene start and end points. Then representative frames are chosen from each scene, the telecine is stopped on the selected frames representative of the scene, and time is spent optimising the grading for that frame. This is then repeated for the remaining scenes of the film. The function of the system is to record in a computer type memory the scene change points, and also the settings of grading for each of the scenes. After the `grading` pass has finished, the film is then transferred to videotape, at normal viewing rate (25 frames per second). In this `playback` mode the programmer uses the vertical interval of the video system format to change the grading settings, ready for the new scene if necessary. This scene by scene colour correction is taught in U.S. Pat. No. 4,096,523 of Armand Belmares-Sarabia et al.
Currently, such telecine machines produce pictures of the same resolution as is currently broadcast, namely 525 line pictures in the North American territories, and 625 line pictures in Europe and other areas. These broadcast standards require respectively the production of 30 frames per second or 25 frames per second. The present telecine machines are capable of working in what is referred to as `real time`. This means that pictures can be produced at the same rate as broadcast.
There have been for many years experimental telecine systems that have produced `High Definition` pictures. These are typically 1250 line pictures in European areas and 1125 or 1050 line pictures in North America.
The data rate for such systems operating in real time is significantly higher than a `standard` definition system. Although this presents problems in the electronics areas, by careful design and high cost this can be overcome. Typically, this increase in data rate is about five times, as there are approximately five times as many pixels in a high definition picture as in a standard definition one.
FB-A-2 243 264 of Rank Cintel discloses a proposal to overcome this difficulty by operating the telecine at a standard definition rate, and to take therefore approximately five times as long to produce one scanned picture of High Definition than of standard definition. The document covers techniques including `sectioning` a high definition frame into several standard definition frames, and also techniques for `interleaving` pixels in typically a 2.times.2 pattern between the four (nominal) standard definition scans.
In some modes of implementation, the telecine may have a `reconstituting` store in it, together with many frames of storage. This allows the non-real time transfer to film material, in which the separate standard definition data rate pictures are assembled into a High definition buffer, and from there stored into a multi frame buffer to build up a sequence of many seconds of video in High definition. This can then be `downloaded` in real time bursts of e.g. 20-30 seconds to a real time high definition video tape recorder.